Conventionally, acid gas components are removed using large absorption columns. These columns are designed to handle a gas feed at a certain flow rate and acid gas content. However changes to the feed conditions cause problems in operation and the absorber may have to be substantially modified to attain satisfactory or optimum performance. Problems where modification is required include, but are not limited to: an increase in the volumetric sour gas flow rate; a requirement for a lower acid gas concentration in the treated gas; a lower solvent circulation rate for the same level of purification; an increase in the acid gas concentration in the feed gas; any combination of the above. These problems with existing plants no longer being able to cope with changed working requirements may be summarised as bottlenecking and their solution as de-bottlenecking.
Modifications to the existing absorption columns and the associated apparatus are expensive and time consuming and many of the above variables can change on a regular basis. One of the current solutions employed to address the problem of needing to increase acid gas treating capacity is to change the solvent employed. However, this is not always appropriate and can introduce secondary problems such as regeneration considerations and corrosion problems. Another solution is to change the column internals from, for example, plates to random or structured packing. This option only has limited capacity for increasing the acid gas removal due to the overall size of the column.
The present invention therefore provides a method for increasing the acid gas absorption capacity of an existing plant and thereby de-bottlenecking plants.
A further problem with plants which have become bottlenecked is that hydrocarbons and carbon dioxide may become entrained and/or absorbed in the acid gas solvent (e.g. amine) and are therefore subsequently fed to the downstream treatment units such as a Claus sulphur recovery unit. These additional components in the feed to the Claus unit reduce the efficiency of the de-sulphurisation plant and may cause an additional bottleneck further down the process. There are also additional loads on the system involved in pumping this extra gas round the acid-gas solvent regeneration system and de-sulphurisation plant. This may overload the existing pumps and require the addition of more or replacement pumps.